ISLE DE JEAN CHARLES, La. — Each morning at 3:30, when Joann Bourg leaves the mildewed and rusted house that her parents built on her grandfather’s property, she worries that the bridge connecting this spit of waterlogged land to Louisiana’s terra firma will again be flooded and she will miss another day’s work.

Ms. Bourg, a custodian at a sporting goods store on the mainland, lives with her two sisters, 82-year-old mother, son and niece on land where her ancestors, members of the Native American tribes of southeastern Louisiana, have lived for generations. That earth is now dying, drowning in salt and sinking into the sea, and she is ready to leave.

With a first-of-its-kind “climate resilience” grant to resettle the island’s native residents, Washington is ready to help.

“Yes, this is our grandpa’s land,” Ms. Bourg said. “But it’s going under one way or another.”

One of those grants, $48 million for Isle de Jean Charles, is something new: the first allocation of federal tax dollars to move an entire community struggling with the impacts of climate change. The divisions the effort has exposed and the logistical and moral dilemmas it has presented point up in microcosm the massive problems the world could face in the coming decades as it confronts a new category of displaced people who have become known as climate refugees.

“We’re going to lose all our heritage, all our culture,” lamented Chief Albert Naquin of the Biloxi-Chitimacha-Choctaw, the tribe to which most Isle de Jean Charles residents belong. “It’s all going to be history.”

Around the globe, governments are confronting the reality that as human-caused climate change warms the planet, rising sea levels, stronger storms, increased flooding, harsher droughts and dwindling freshwater supplies could drive the world’s most vulnerable people from their homes. Between 50 million and 200 million people — mainly subsistence farmers and fishermen — could be displaced by 2050 because of climate change, according to estimates by the United Nations University Institute for Environment and Human Security and the International Organization for Migration.

“The changes are underway and they are very rapid,” Interior Secretary Sally Jewell warned last week in Ottawa. “We will have climate refugees.”

But the problem is complex, said Walter Kaelin, the head of the Nansen Initiative, a research organization working with the United Nations to address extreme-weather displacement.

“You don’t want to wait until people have lost their homes, until they flee and become refugees,” he said. “The idea is to plan ahead and provide people with some measure of choice.”

The Isle de Jean Charles resettlement plan is one of the first programs of its kind in the world, a test of how to respond to climate change in the most dramatic circumstances without tearing communities apart. Under the terms of the federal grant, the island’s residents are to be resettled to drier land and a community that as of now does not exist. All funds have to be spent by 2022.

“We see this as setting a precedent for the rest of the country, the rest of the world,” said Marion McFadden, who is running the program at the Department of Housing and Urban Development.

But even a plan like this — which would move only about 60 people — has been hard to pull off. Three previous resettlement efforts dating back to 2002 failed after they became mired in logistical and political complications. The current plan faces all the same challenges, illustrating the limitations of resettlement on any larger scale.

For over a century, the American Indians on the island fished, hunted, trapped and farmed among the lush banana and pecan trees that once spread out for acres. But since 1955, more than 90 percent of the island’s original land mass has washed away. Channels cut by loggers and oil companies eroded much of the island, and decades of flood control efforts have kept once free-flowing rivers from replenishing the wetlands’ sediments. Some of the island was swept away by hurricanes.

What little remains will eventually be inundated as burning fossil fuels melt polar ice sheets and drive up sea levels, projected the National Climate Assessment, a report of 13 federal agencies that highlighted the Isle de Jean Charles and its tribal residents as among the nation’s most vulnerable.

Already, the homes and trailers bear the mildewed, rusting scars of increasing floods. The fruit trees are mostly gone or dying thanks to saltwater in the soil. Few animals are left to hunt or trap.

Violet Handon Parfait sees nothing but a bleak future in the rising waters. She lives with her husband and two children in a small trailer behind the wreckage of their house, which Hurricane Gustav destroyed in 2008.

The floods ruined the trailer’s oven, so the family cooks on a hot plate. Water destroyed the family computer, too. Ms. Parfait, who has lupus, is afraid of what will happen if she is sick and cannot reach a doctor over the flooded bridge.

Ms. Parfait, who dropped out of high school, hopes for a brighter future, including college, for her children, Heather, 15, and Reggie, 13. But the children often miss school when flooding blocks their school bus.

“I just want to get out of here,” she said.

Still, many residents of Isle de Jean Charles do not want to leave. Attachment to the island runs deep. Parents and grandparents lived here; there is a cemetery on the island that no one wants to abandon. Old and well-earned distrust of the government hangs over all efforts, and a bitter dispute between the two Indian tribes with members on the island has thwarted efforts to unite behind a plan.

“Ain’t nobody I talk to that wants to move,” said Edison Dardar, 66, a lifelong resident who has erected handwritten signs at the entrance to the island declaring his refusal to leave. “I don’t know who’s in charge of all this.”

Whether to leave is only the first of the hard questions: Where does everyone go? What claim do they have to what is left behind? Will they be welcomed by their new neighbors? Will there be work nearby? Who will be allowed to join them?

“If you have a hard time moving dozens of people,” he continued, “it becomes impossible in any kind of organized or fair way to move thousands, or hundreds of thousands, or, if you look at the forecast for South Florida, maybe even millions.”

Louisiana officials have been coping with some of the fastest rates of land loss in the world — an area the size of Delaware has disappeared from south Louisiana since the 1930s. A master plan that is expected to cost tens of billions of dollars envisions a giant wall of levees and flood walls along the coast.

But some places, like the island, would be left on the outside. For those communities, wholesale relocation may be an effective tool, if a far more difficult and costly one.

“That’s one of the things we need to learn from the creation of this model, which is how to do it economically,” said Pat Forbes, the executive director of the state’s Office of Community Development, the agency in charge of administering the federal climate grant.

A vast majority of the $1 billion disaster-resilience grant program is spent on projects to improve infrastructure, like stronger roads, bridges, dams, levees and drainage systems, to withstand rising seas and stronger storms.

But experts see places like Isle de Jean Charles as lost causes.

“We are very cognizant of the obligation to taxpayers to not throw good money after bad,” Ms. McFadden of the Department of Housing and Urban Development said. “We could give the money to the island to build back exactly as before, but we know from the climate data that they will keep getting hit with worse storms and floods, and the taxpayer will keep getting hit with the bill.”

With door-to-door visits, the state is only beginning to find out what the residents want in a new plan, Mr. Forbes said.

The location of the new community has not been chosen. Chiefs of the two tribes present on the island — the Biloxi-Chitimacha-Choctaw and the United Houma Nation — have debated who would be allowed to live there beyond the islanders themselves, and whether some islanders could resettle elsewhere. One of the planners involved in the resettlement suggested a buffer area between the new community and its surrounding neighborhood to reduce tension. Chief Naquin wants a live buffalo on site.

What has been decided, and what was essential for the islanders’ support, is that the move be voluntary.

“I’ve lived my whole life here, and I’m going to die here,” said Hilton Chaisson, who raised 10 sons on the island and wants his 26 grandchildren to know the same life of living off the land.

He conceded that the flooding has worsened, but, he said, “we always find a way.”